2.54 describe the structure of arteries, veins and capillaries and understand their roles

2.54 •arteries: carry blood away from the heart (arteries away)

        •capillaries: exchange of materials at the tissues

        •veins: carry blood to the heart

        •arteries: •heart pumps high pressure blood so the artery walls are strong and elastic 

                       •the walls are thick compared to the middle (lumen) for strength 

        •capillaries: •arteries branch into capillaries 

                           •they carry blood close to every cell to exchange substances

                           •permeable walls, allowing substances to diffuse 

                           •supply food and oxygen, and take away wastes like carbon dioxide 

                           •walls are one cell thick, increasing the rate of diffusion  

         •veins: •capillaries join to form veins

                     •blood has lower pressure, so have thinner walls than the artery

                     •have a bigger lumen than the arteries, to assist blood flow despite the pressure

                     •have valves to keep the blood flowing in one direction